<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
     手机号码：<input type="number">
  <button>发送</button>
  <script>
   var btn =  document.querySelector("button")
   var time = 5
   
    btn.addEventListener("click",function(){
          btn.disabled = true
    var timer = setInterval(function(){
        if(time >0 )
        {
            btn.innerHTML = "还剩" + time + "秒"
            time--
        }else{
            btn.disabled = false
            clearInterval(timer)
             btn.innerHTML="按钮"

        }

    },1000)


    })
  </script>
</body>
</html>